Fat-soluble vitamins such as vitamin K, vitamin A, coenzyme Q and vitamin D are known to be unstable to light, etc. Thus various methods have been attempted to stabilize those fat-soluble vitamins in formulating pharmaceutical preparations.
For the stabilization of vitamin K.sub.1 (phylloquinone) and vitamin K.sub.2 (menaquinone) having hemostasis-enhancing action (called antihemorrhagic vitamins) which are known to be very unstable to light, attempts have been made wherein vitamin K dissolved in an oil and fat is encapsulated into a colored capsule for light shielding and wherein a variety of stabilizers are incorporated into vitamin K. Japanese Patent Publication No. 4062/1967 discloses a method for the stabilization of menadione (vitamin K.sub.3) or its sodium bisulfite solution using as a stabilizer one or more of caffeine, theobromine, theophylline or their soluble salts.
Further, measures have been taken for pharmaceutical preparations of vitamin A or coenzyme Q, such as use of a variety of stabilizers or protection from light or oxygen by means of encapsulation.
However the above attempts have been accomplished with unsatisfactory results.
Thus the present invention results from efforts to develop a new stabilizer for fat-soluble vitamins.